Method for correcting the temperature of steel at the end of the refining process



Nov. 4, 1969 J. LEDUNE ETAL 3,476,550

METHOD FOR CORRECTING THE TEMPERATURE OF STEEL AT THE END OF THE REFINING PROCESS Filed July 6, 1966 kqs. of lime United States Patent METHOD FOR CORRECTING THE TEMPERATURE OF STEEL AT THE END OF THE REFINING PROCESS Jacques Ledune, Marchienue-au-Pont, and Gaul Nilles, Embourg -Belgium, assignors to Centre Nationale de R'cherches Metallurgiques, Brussels, Belgium, Socrete Anonyme des Forges de la Providence, Marchienneau-Pont, Belgium, both Belgian companies and Mannesmann, Aktiengesellschaft, Dusseldorf, Germany, a German company Filed July 6, 1966, Ser. No. 563,287 Claims priority, application Belgium, Nov. 17, 1965, 672,472; Luxembourg, July 7, 1965, 49,012; Dec. 15, 1965, 50,072

Int. Cl. C21c 5/28 U.S. C]. 75-52 2 Claims ABSTRACT OF THE DISCLOSURE A method for adjusting the temperature of steel in a converter at the end of a refining process consists of adding lime to the metal and blasting in oxygen while causing the converter to rotate about its axis.

The present invention concerns a method by which it is possible to correct the temperature of liquid steel :at the,.end of the process of refining pig iron, and in particular phosphorus-containing pig iron.

The important repercussions that the temperature of the steel at the end of the refining process has on the casting process, and consequently on the quality and appearance of the ingots obtained, particularly in the case of continuous casting, is known.

Generally speaking, with the use of the customary techniques it is difficult to obtain with sufiicient accuracy a predetermined temperature of the steel at the end of therefining process, and in actual fact the accuracy obtained with the said customary techniques is a maximum of :25 C., which is inadequate. In actual practice, the final temperature is corrected by short periods of renewed blasting, but this technique is not very reliable and there is the risk of bringing about an exaggerated oxidation state in the metallic bath.

The aim of the present invention is a process making possible an easy and satisfactory correction of the temperature of liquid steel at the end of the refining process, for use in the manufacture of steel by the refining of pig iron, in particular phosphorus-containing pig iron, by means of substantially pure oxygen (hereinafter referred to as oxygen) blasted from above the bath into a solid bottomed converter that can rotate about its longitudinal axis.

The method of the invention consists essentially in that at the end of the refining operation the temperaure of the metallic bath is regulated by the addition of lime and by blasting with oxygen while the converter is rotating about its longitudinal axis. The addition of lime to the steel leads to a cooling of the metal that can be calenlisted in accordance with the proportions and temperatures of the materials, whereas the blasting with oxygen allows a small rise in the temperature of the bath. The addition of lime simultaneously with the blasting-in of oxygen accordingly makes it possible to regulate the temperature accurately, as the contrary efiects of the two actions allow easy checking of the operation of correcting the temperature of the bath.

The application of the present method is of particular interest when refining takes place in two separate phases by deslagging, with the converter rotating about its longitudinal axis during the second phase, and is also of interest when the refining operation is conducted without intermediate deslagging, in a single phase, at the end of which the converter is caused to rotate about its longitudinal axis, the single deslagging operation constituting the final deslagging.

Excellent homogenisation of the bath is obtained by the method of the invention, with the result that the steel can be cast in the ladle at a lower temperature, by approximately 20 C., than that generally necessary with steels that have not been subjected to the temperature correctionv following the method described in this pattern.

If necessary, a determined temperature correction can be carried out by keeping the oxygen rate of flow fixed, and by regulating the amount of lime added, or by keeping the amount of lime to be added to the bath at a fixed rate, and by regulating the rate of flow of the oxygen.

Accordingly it is possible to add lime to the bath in an amount greater than the amount normally required to ensure the desired cooling, for example with the purpose of obtaining a thicker slag and furthermore to resist exaggerated cooling by blasting the bath with oxygen. A more thorough dephosphoration of the bath is possible with this method of operation.

Using the method of the invention, it is possible to obtain steel temperatures at the end of the refining process which do no deviate by more than 10 C. from the temperature desired.

In an advantageous embodiment of the method described above, it is possible to obtain good mixing conditions and physicochemical equilibrium between the slag and the metallic bath while keeping the rotation speed of the appratus at the end of the refining process at a low value, equal to or less than 10 rotations per minute. This variation, as far as concerns the composition of the steels worked in this way, applies more particularly to mild steels i.e. steels with carbon content in the bath lower than 0.15% and preferably between 0.05% and 0.1%.

In another embodiment of the method, oxygen and lime are added to the bath through the same lance, thus making it possible to avoid the introduction of undesirable nitrogen at the teeming pot.

The amounts of lime and of oxygen that is necessary to add to or to blast into the steel to correct its temperature can be determined from charts such as the one shown in the accompanying drawing. The temperature deviations (in degrees centigrade) in relation to the desired temperature of the steel at the end of the refining process are plotted on the abscissa in this diagram, whilst on the ordinate the amounts of lime are shown, which it is necessary to add to the steel to reduce the said deviations. The said amounts are a function of the rates of flow of oxygen blasted into the bath, and are shown on the chart by the straight lines B (no blasting of oxygen) and A (rate of flow of 50 mfi/minute).

By way of example, there is shown on the drawing the corrections of temperature obtained by the addition of 700 kgs. of lime in a 35 ton converter. Without blasting-in oxygen, the temperature of the steel is lowered by 45 C.; when simultaneously with the addition of the lime the blasting of oxygen takes place at the rate of 50 m. /minute, the temperature reduction is only 25 C.

Accordingly it can be seen that in the case of blasting with oxygen, the influence of a determined addition of lime on the decrease in the temperature of the bath is less than in the case where blasting does not take place. The accuracy of the correction is accordingly greater where blasting takes place.

We claim:

1. In a method of accurately controlling the temperature of molten steel at the end of the refining process whereby the temperature of said molten steel does not 10 deviate by more than about 10 C. from said desired temperature.

2. A method as claimed in claim 1, in which both said lime and substantially pure oxygen are simultaneously blown into said rotating converter through a lance.

References Cited UNITED STATES PATENTS 3,076,703 2/1963 Metz 75-52 3,136,626 6/1964 Decamps 7552 FOREIGN PATENTS 492,740 9/1938 Great Britain. 904,868 8/1962 Great Britain. 1,007,410 10/1965 Great Britain.

L. DEWAYNE RUTLEDGE, Primary Examiner G. K. WHITE, Assistant Examiner US. Cl. X.R. 7554 

